Communication systems, in general, and cellular systems, in particular, are extensively used to provide wireless communication services to a wide array of mobile subscribers. For example, European Telecommunication Standard Institute (ETSI) has specified a Global Standard for Mobile Communication (GSM) that uses time division multiple access (TDMA) to communicate control, voice and text information over radio frequency (RF) channels. In the U.S., Telecommunication Industry Association (TIA) has published a number of Interim Standards, such as IS-136, that define various versions of digital advanced mobile phone service (D-AMPS), with the capability of transmitting voice and data to subscribers. Generally, these systems include scattered base stations that communicate via corresponding transceivers with mobile stations over uplink and down link RF channels. During normal operation, the base stations transmit communication signals to the mobile stations over downlink RF channels and receive communication signals from the mobile stations over uplink RF channels. Similarly, the mobile stations include transceivers that transmit communication signals over the uplink RF channels and receive communication signals over the downlink RF channels.
Over the years, communication system operators have recognized that quality of communication over RF channels is of utmost importance. The communication quality over the RF channels is affected by the condition of various radio elements, i.e., the antenna equipment and transceivers, of the base station. Therefore, system operators regularly monitor the operating condition of their system's base stations, in order to offer their services with a satisfactory quality level. The regular monitoring of base station operating condition, which involves performing a battery of tests and measurements, is costly. As a result, the systems operators are constantly searching for ways to reduce their operating cost, without sacrificing the quality of the offered services.
Conventionally, test equipment, which are capable of establishing wireless communication with the base station for emulating communication path with mobile stations, are used to perform the test and measurements. Under one arrangement, a technician visits cell sites in order to perform manual measurements using the test equipment. The labor cost of performing the tests manually, however, is high, with such cost increasing as the size of a system and/or the number of its cell sites become larger. Therefore, less costly automated test and measurements methods are preferred, because they eliminate the need for visiting the cell sites, or, alternatively, such automated tests could allow the operator to more intelligently decide whether a site should be visited or not. Most conventional automated tests utilize costly dedicated test equipment that are incorporated in the base stations.
Another conventional automated test method known as Radio Frequency Test Loop (RFTL) provides a loop between the transmitter and receiver paths of a base station. In a test mode, RF switches connected to suitable attenuators couple the transmitter of the base station to its receiver to test base stations receiver and transmitter paths. The RFTL, however, provides for the testing of some but not all elements of the base station. For example, the RFTL method does not include base station antenna and feeder in the test loop. As a result, if an external object, which is positioned near the base station, impedes propagation of RF waves to and from the base station, or if the antenna has been damaged, the RFTL method is unable to accurately detect reception quality.
Therefore, there exists a need for a low cost test method for accurately checking the transmitting and receiving capabilities of scattered base stations of a communication system.